Car Stalling Immediately After Starting - Pls Help

[SQ13]

Edit: Added updates 1 and 2 to the OP. Resolution in update 2

Lately I’ve been having some issues with occasional rough idling and misfiring. This morning, I experienced a shit ton of misfiring and a couple of stalls after a cold start and driving about 100 yards. After I unplugged the MAF, the car ran smoothly.

I’ve tried two MAF sensors so far, and have a third I can throw on. The first is a Bosch MAF sensor that is less than two years old/<5k miles. Because of the issues I’ve been having, last week I swapped in my old MAF that was working fine previously. However, I’m getting the same code with both sensors - “29 DME: Signal, air-mass flow sensor.” The 4D code popped up after I unplugged the MAF. All of the intake parts are installed correctly, so there shouldn’t be any leaks. Am I overlooking something?



Update 1 (09MAR23):
Bumping this again. I replaced one of the throttle position sensors, and the codes disappeared for a few hundred miles. Drove the car 140 miles last night with no issues. This morning, the car stalled immediately after I started it two times.

Car is at 107k miles. The O2 sensors are fairly new, and I don’t think both pre-cat sensors would fail at the same time (post-cat sensors removed). Spark plugs (20k miles), ignition coils (5k miles), fuel filter (17k miles), and fuel pump (14k miles) all should be good. Fuel pump is priming.

Fuel pump relay maybe?

Edit: Forgot to disconnect the MAF to see if that helps. Will try that after work..pretty sure I have one of the older sensors installed.




Update 2 (15MAR23): Drove to a DIY shop to install the O2 sensors, and I pulled a ton of codes on the way there (pictured below). Car was running extremely poorly. Intake elbow and everything in front were removed again for inspection, then reinstalled. Both pre-cat oxygen sensors were replaced with new Bosch sensors from Autozone. Post-cat oxygen sensors and EGT were removed and coded out years ago due to previous catless setup. Cleared adaptations, and the car is running smoothly now. No codes in the 10-15 miles I’ve driven it, but I will check again after a 140 mile drive this weekend. I’m very surprised that both oxygen sensors seem to have failed at around the same time…maybe a bad TPS sensor led to poor AFR, which killed the oxygen sensors.

I’m installing a CSL intake in the next couple of weeks, so the plan is to replace some stuff preventively and inspect other parts while the intake is out to ensure the car runs perfectly when it’s time to dyno tune the car. Installing the following parts:
OE NGK spark plugs (30k mile NGK Iridum plugs currently)
Crankcase vent valve + hose
Bosch 62431 fuel injectors and o-rings
Crankcase breather hose
TPS at throttle actuator

Inspect idle control valve hoses. Air line connecting pipe o-rings (16k miles), ignition coils (5k), and front TPS (<1k) should be fine.

[sapote]

Unplugged MAF running better means engine was running too lean.
Install MAF back, get to operating temperature and read MAF air flow rate in grams/second at idle. Should be around 4g/s

[eacmen]

Did you clear the codes after plugging MAF back in?

Reset throttle adaptations?

What are your fuel trim values?


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[SQ13]

Unplugged MAF running better means engine was running too lean.
Install MAF back, get to operating temperature and read MAF air flow rate in grams/second at idle. Should be around 4g/s

Did you clear the codes after plugging MAF back in?

Reset throttle adaptations?

What are your fuel trim values?

Codes were cleared after MAF was plugged back in. With AC off, at idle the MAF flow rate was about 4.9-5.2 g/s (converted from kg/h). Throttle adaptations were reset. Not sure how to find the fuel trim values.

Swapping in the third MAF seemed to fix the issue for a couple of days, but now the car is stalling again. The error “94 DSC: CAN data fault from DME/DDE” popped up as well as the 29 DME error that keeps appearing.

Did some searching, and it appears that one of the TPS/TB may be the culprit? I’m ordering two throttle position sensors, and if they don’t help, I can look into replacing the gas pedal. Not sure what other parts I should throw at it to make it run normally again…the car has 106k miles on it, but the following stuff is fine: coils, spark plugs, idle control valve, air filter.

[SQ13]

Bumping this again. I replaced one of the throttle position sensors, and the codes disappeared for a few hundred miles. Drove the car 140 miles last night with no issues. This morning, the car stalled immediately after I started it two times.

Car is at 107k miles. The O2 sensors are fairly new, and I don’t think both pre-cat sensors would fail at the same time (post-cat sensors removed). Spark plugs (20k miles), ignition coils (5k miles), fuel filter (17k miles), and fuel pump (14k miles) all should be good. Fuel pump is priming.

Fuel pump relay maybe?

Edit: Forgot to disconnect the MAF to see if that helps. Will try that after work..pretty sure I have one of the older sensors installed.

[duracellttu]

With those codes I’d look at the fuel pump. See if it primes when putting the key is position two. You should be able to hear it. Pop off the back seat to hear it better.

You might have a vacuum leak somewhere. I had the same symptom a while back but with no codes. Ended up being the connection from the air rail to the ICV, but any vacuum leak could cause it. Double check all the connections and rubber hoses.

[SQ13]

The OE fuel pump has 14k miles on it and is priming normally.

I didn’t find any loose connections a couple of weeks ago, but I’ll look again.

[sapote]

what are MAF rate in g/s and rpm at hot idle? You should get the OBD2 Veepeak and display on the app, and make a log file with fuel trim data, rpm, temp, O2 signals, etc.

[SQ13]

what are MAF rate in g/s and rpm at hot idle? You should get the OBD2 Veepeak and display on the app, and make a log file with fuel trim data, rpm, temp, O2 signals, etc.

Can’t gather any data right now bc the car is stalling immediately after starting. I’ll have to check for vacuum leaks this weekend and install new MAF sensor, and hopefully the car will run long enough to pull that data. Is it possible to make a log file using the Schwaben tool or INPA?

I believe my issues started appearing after I installed new headers. After looking thru the thread below, I’m starting to think I may have damaged the O2 sensors. First step is to get the car to run. Then, I should be able to figure out what values the various sensors are putting out. I do have a spare set of pre-cat O2 sensors that I can throw on.

https://nam3forum.com/forums/forum/main-forum/e46-2001-2006/31731-primary-o2-problems-after-euro-header-install/page3

[Speed Monkey]

SQ13, you mentioned fuel pump, that would be one of my top usual suspects. There is no sensor tied to a fuel pump, so when it runs erratically, unless a fuel pressure gauge can be plumbed-in and monitored inside the cabin when you’re road-testing the car, seeing what’s happening will be like someone telling you to, “take two aspirin and call me in the morning if you don’t feel well.” If you go that route in the fuel system, remove the rear seat, then shine a good flashlight into the tank; if you see lots of metallic glitter collected in the tank, that is a sure sign of the pump is self destructing. Replace it. If there is no metallic glitter, replace the fuel filter. A clogged filter can wreak all sorts of runability problems.

[SQ13]

SQ13, you mentioned fuel pump, that would be one of my top usual suspects. There is no sensor tied to a fuel pump, so when it runs erratically, unless a fuel pressure gauge can be plumbed-in and monitored inside the cabin when you’re road-testing the car, seeing what’s happening will be like someone telling you to, “take two aspirin and call me in the morning if you don’t feel well.” If you go that route in the fuel system, remove the rear seat, then shine a good flashlight into the tank; if you see lots of metallic glitter collected in the tank, that is a sure sign of the pump is self destructing. Replace it. If there is no metallic glitter, replace the fuel filter. A clogged filter can wreak all sorts of runability problems.

I’d be surprised if the fuel pump and/or the fuel filter went bad at ~15k miles, but it’s a possibility. I’ll try to see if someone can help me check the pressure at the fuel filter.

New O2 sensors are on order since I don’t know exactly how many miles they’ve been used for. I’ll install TPS under the intake when I remove the intake…also a good time to check all hoses/lines for vacuum leaks. I think those will be the next steps once I can get the car to run and check values via scanner.